There can be emotional cheating as well. There are people going online and talking to people other than their spouses or those they are with and stating there is no issue with it because they're not cheating. But it still is, they're removing that emotional bond away from their relationship and putting it to someone outside of it. That is still cheating even if there is never any physical contact.
Cheating is cheating and there will never be a time that it is "okay" and unless you feel remorse, guilt, and disgust for what you did then I don't think you will ever be able to change that part of who you are will be stuck repeating it over and over again. Especially, if it's in the scenario that you presented in the first post.
A guy cheats on someone he is currently with but then goes after the new person. There is no time in between to feel the sorrow and guilt of what you did. It becomes a cycle that I believe cannot be broken until we take the time to step away from everyone else, view what we're doing wrong, and realize what is wrong with us to realize why it's happening. Not think about what the other person did or didn't do.